Organic semiconductor polymer, composition for organic semiconductor material, and photovoltaic cell

ABSTRACT

An organic semiconductor polymer having a structural unit represented by the following Formula (I), a composition for organic semiconductor material, a photovoltaic cell and a polymer, 
     
       
         
         
             
             
         
       
         
         
           
             wherein X represents Si, S or O; R 1  represents a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, an aromatic heterocyclic group or an oxygen atom; p represents 0, 1 or 2; herein, the bond between X and R 1  is such that when X is Si, the bond is a single bond, and when X is S, the bond is a double bond. Furthermore, when X is O, p represents 0.

TECHNICAL FIELD

The present invention relates to an organic semiconductor polymer, a composition for organic semiconductor material and a photovoltaic cell.

BACKGROUND ART

Organic semiconductor polymers have been a subject of active research in recent years in the field of organic electronics, and the polymers are used in organic electroluminescent elements that emit light when electricity is passed, organic photoelectric conversion elements that generate power when irradiated with light, organic thin film transistor elements that control the amount of current or the amount of voltage, and the like. In such an element, similarly to an inorganic semiconductor material, use is made of an organic semiconductor material obtained by combining a p-type conductive semiconductor material, which is an electron donor material, and an n-type conductive semiconductor material, which is an electron acceptor material.

In recent years, since fossil energy of petroleum and the like emit carbon dioxide to the atmosphere, for the purpose of global environment preservation with the suppression of global warming, there is an increasing demand of solar cells. Known examples of organic solar cells that use organic photoelectric conversion elements include a wet type dye-sensitized solar cell (Gräetzel cell) and a total solid type organic thin film solar cell. Since the latter does not use an electrolyte solution, there is no need to take evaporation of this electrolyte solution or liquid leakage into consideration, the solar cell can be made flexible, and the structure of the solar cell or production thereof is more convenient than that of the former.

However, the photoelectric conversion efficiency of organic thin film solar cells is still insufficient. The photoelectric conversion efficiency is calculated by short circuit current (Jsc)×open circuit voltage (Voc)×fill factor (FF); according to which, in order to increase this efficiency, an increase in the open circuit voltage is also needed along with an increase in the short circuit current. The short circuit current is increased when an organic semiconductor material having high solubility and carrier mobility (for example, a compound having a fluorene structure or a silafluorene structure) is used. The open circuit voltage, which is said to be connected with the difference between the HOMO energy level of the p-type conductive semiconductor material and the LUMO energy level of the n-type conductive semiconductor material, is raised when this difference is increased. Furthermore, in the case of an organic solar cell, in order to increase the efficiency, it is efficient to absorb more light of a region of longer wavelengths (650 nm to 800 nm) than the wavelengths of sunlight. Therefore, band gap narrowing is desirable. It is expected that the enhancement of luminescence efficiency, that is, enhancement of the power efficiency of organic electroluminescent lighting for an organic electroluminescent element.

On the other hand, studies on organic semiconductor polymers as p-type conductive semiconductor materials, which are electron donor materials, are in active progress. For example, Patent Literature 1 suggests a polymer having a particular cyclopentadithiazole structure, and Patent Literature 2 suggests a polymer having a particular silacyclopentadithiophene structure. However, in both cases, the conversion efficiency of the solar cell using the above-mentioned polymers is not necessarily sufficient, and these polymers are not satisfactory in terms of durability, and particularly in terms of durability in the presence of oxygen.

CITATION LIST Patent Literatures

-   Patent Literature 1: WO 08/067,023 -   Patent Literature 2: JP-T-2010-507233 (“JP-T” means searched and     published

SUMMARY OF THE INVENTION Technical Problem

An object of the present invention is to provide an organic semiconductor polymer which has excellent photoelectric conversion efficiency and is excellent in durability, and particularly in durability in the presence of oxygen, and which has a smaller decrease in the photoelectric conversion efficiency even in the case where the cell size is increased. Particularly, it is an object of the present invention to achieve a good balance between band gap narrowing conducted to enhance the photoelectric conversion efficiency and an enhancement of durability, and then to provide an organic semiconductor polymer which has a reduced cell size-dependency of the photoelectric conversion efficiency. Furthermore, another object of the present invention is to provide a composition for organic semiconductor materials containing such an organic semiconductor polymer, and a photovoltaic cell (particularly, an organic thin film solar cell) having the polymer or the composition. Moreover, still another object of the present invention is to provide a polymer which is useful for organic electronic devices such as an organic electroluminescent element and an organic thin film transistor element.

Solution to Problem

The inventors of the present invention conducted thorough investigations in order to achieve the problems described above, and as a result, they paid attention to the deep HOMO energy level of organic semiconductor polymers for an enhancement in the efficiency of organic semiconductor polymers, particularly an enhancement in durability, and investigated various compounds having such a polymer structure. Thereby, the inventors found that an organic semiconductor polymer having a particular structure can achieve a balance between wavelength lengthening of the absorption wavelength in the band gap narrowing of a photovoltaic cell, and an enhancement of durability. Particularly, for a good balance between the photoelectric conversion efficiency and durability, the condensation arrangement and the kind of three rings are important, and when the thiazole structure is linked to a particular element, the HOMO energy level can be made deeper. Also, in regard to the prevention of a decrease in the photoelectric conversion efficiency by the dependency on cell size, although it is not clearly known, it is thought that by adopting the relevant structure of the invention, the π-π stacking properties between polymer molecules are enhanced, and it is made easier to adopt a molecular arrangement that is preferable for a wide cell area. As a result, it was found that efficient battery characteristics are exhibited in a wide region.

The present invention has been achieved based on those finding.

All of the problems of the present invention can be solved by the following means.

<1> An organic semiconductor polymer having a structural unit represented by the following Formula (I):

wherein X represents Si, S or O; R¹ represents a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, an aromatic heterocyclic group or an oxygen atom; p represents 0, 1 or 2; herein, the bond between X and R¹ is such that when X is Si, the bond is a single bond, and when X is S, the bond is a double bond. Furthermore, when X is O, p represents 0, and when p is 2, two R¹'s may be the same or different from each other, or two R¹'s may bond with each other to form a ring.

<2> The organic semiconductor polymer described in the above item <1>, wherein the structural unit represented by Formula (I) is a structural unit represented by Formula (I-1):

wherein R¹′ and R¹″ each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group or an aromatic heterocyclic group; and R¹′ and R¹″ may bond with each other to form a ring.

<3> The organic semiconductor polymer described in the above item <1>, wherein the structural unit represented by Formula (I) is a structural unit represented by Formula (I-2):

wherein p′ represents 0, 1 or 2.

<4> The organic semiconductor polymer described in the above item <1>, wherein the structural unit represented by Formula (I) is a structural unit represented by Formula (I-3):

<5> The organic semiconductor polymer described in any one of the above items <1> to <4>, wherein the organic semiconductor polymer is a co-polymer. <6> The organic semiconductor polymer described in any one of the above items <1> to <4>, wherein the organic semiconductor polymer is a co-polymer which further includes a structural unit represented by the following Formula (II):

wherein Z¹ and Z² each independently represent S, O, Se or Te; Y represents C(R²¹) or N; R and R²¹ each independently represent a hydrogen atom or a substituent.

<7> A composition for organic semiconductor material, including the organic semiconductor polymer described in any one of the above items <1> to <6> and an n-type organic semiconductor molecule.

<8> The composition for organic semiconductor material described in the above item <7>, wherein the n-type organic semiconductor molecule is fullerene or a derivative thereof.

<9> The composition for organic semiconductor material described in the above item <8>, wherein the fullerene or a derivative thereof is a phenyl-C₆₁-butyric acid ester, a diphenyl-C₆₂-bis(butyric acid ester), a phenyl-C₇₁-butyric acid ester, a phenyl-C₈₅-butyric acid ester, or a thienyl-C₆₁-butyric acid ester. <10> A photovoltaic cell including the organic semiconductor polymer or the composition for organic semiconductor material described in any one of the above items <1> to <9>. <11> A photovoltaic cell including a layer containing the organic semiconductor polymer or the composition for organic semiconductor material described in any one of the above items <1> to <9>, between a first electrode and a second electrode. <12> The photovoltaic cell described in the above item <11>, including a hole transport layer between the first electrode and the layer containing the organic semiconductor polymer or the composition for organic semiconductor material. <13> The photovoltaic cell described in the above item <11> or <12>, including an electron transport layer between the second electrode and the layer containing the organic semiconductor polymer or the composition for organic semiconductor material. <14> The photovoltaic cell described in any one of the above items <11> to <13>, wherein the first electrode is a transparent electrode. <15> The photovoltaic cell described in any one of the above items <11> to <14>, wherein the second electrode is a metal electrode. <16> A polymer having a structural unit represented by the following Formula (I):

wherein X represents Si, S or O; R¹ represents a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, an aromatic heterocyclic group or an oxygen atom; p represents 0, 1 or 2; herein, the bond between X and R¹ is such that when X is Si, the bond is a single bond, and when X is S, the bond is a double bond. Furthermore, when X is O, p represents 0, and when p is 2, two R¹'s may be the same or different from each other, or two R¹'s may bond with each other to form a ring.

<17> The polymer described in the above item <16>, wherein the structural unit represented by Formula (I) is a structural unit represented by Formula (I-1):

wherein R¹′ and R¹″ each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group or an aromatic heterocyclic group; and R¹′ and R¹″ may bond with each other to form a ring.

<18> The polymer described in the above item <16>, wherein the structural unit represented by Formula (I) is a structural unit represented by Formula (I-2):

wherein p′ represents 0, 1 or 2.

<19> The polymer described in the above item <16>, wherein the structural unit represented by Formula (I) is a structural unit represented by Formula (I-3):

<20> The polymer described in any one of the above items <16> to <19>, wherein the polymer is a co-polymer. <21> The polymer described in any one of the above items <16> to <19>, wherein the polymer is a co-polymer which further includes a structural unit represented by the following Formula (II):

wherein Z¹ and Z² each independently represent S, O, Se or Te; Y represents C(R²¹) or N; R and R²¹ each independently represent a hydrogen atom or a substituent.

Advantageous Effects of Invention

According to the present invention, an organic semiconductor polymer which has excellent photoelectric conversion efficiency and is excellent in durability, and particularly in durability in the presence of oxygen, and which has a smaller decrease in the photoelectric conversion efficiency even in the case where the cell size is increased; a composition for organic semiconductor material containing the organic semiconductor polymer; a photovoltaic cell (particularly, an organic thin film solar cell) including the polymer or the composition; and a polymer can be provided.

MODE FOR CARRYING OUT THE INVENTION

The inventors of the present invention paid attention to the HOMO energy level of organic semiconductor polymers for an enhancement in the efficiency of organic semiconductor polymers, particularly an enhancement in durability, and investigated various compounds having such a polymer structure. Thus, the inventors confirmed that the HOMO energy level of an organic semiconductor polymer is related to Voc (open circuit voltage) of a solar cell so that as this HOMO energy level is lower, Voc increases, and also confirmed that although an organic semiconductor polymer generally tends to be easily oxidized and deteriorated, when the energy level is lowered, the stability to oxidation caused by oxygen in the atmosphere or the like is enhanced. The inventors then found that an organic semiconductor polymer having a particular structure can achieve a balance between wavelength lengthening of the absorption wavelength in the band gap narrowing of a photovoltaic cell, and an enhancement of durability.

A photovoltaic cell containing the organic semiconductor polymer of the present invention has excellent photoelectric conversion efficiency and is excellent in durability, and particularly in durability in the presence of oxygen, and even in the case where the cell size is increased, the photovoltaic cell undergoes a small decrease in the photoelectric conversion efficiency.

<Polymer Having Structure Unit Represented by Formula (I) of Invention>

First, the polymer having a structural unit represented by the following Formula (I) of the present invention will be described.

In Formula (I), X represents Si, S or O; R¹ represents a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, an aromatic heterocyclic group or an oxygen atom; p represents 0, 1 or 2; herein, the bond between X and R¹ is such that when X is Si, the bond is a single bond, and when X is S, the bond is a double bond. Furthermore, when X is O, p represents 0, and when p is 2, two R¹'s may be the same or different from each other, or two R¹'s may bond with each other to form a ring.

The polymer having a structural unit represented by the following Formula (I) of the present invention will be described in detail below.

X represents Si, S or O. X is preferably Si or S, and more preferably Si. R¹ represents a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, an aromatic heterocyclic group or an oxygen atom.

The alkyl group for R¹ is a substituted or unsubstituted, linear or branched alkyl group, and preferably an alkyl group having 1 to 30 carbon atoms. Examples thereof include methyl, ethyl, n-propyl, isopropyl, t-butyl, n-octyl, eicosyl, 2-chloroethyl, 2-cyanoethyl, and 2-ethylhexyl.

The cycloalkyl group for R¹ is a substituted or unsubstituted cycloalkyl group, and preferably a cycloalkyl group having 3 to 30 carbon atoms. Examples thereof include cyclohexyl, cyclopentyl, and 4-n-dodecylcyclohexyl.

The aryl group for R¹ is a substituted or unsubstituted aryl group, and preferably an aryl group having 6 to 30 carbon atoms. Examples thereof include phenyl, p-tolyl, naphthyl, m-chlorophenyl, and an o-hexadecanoylaminophenyl.

The aromatic heterocyclic group for R¹ is a substituted or unsubstituted aromatic heterocyclic group, preferably having 0 to 30 carbon atoms, and preferably being a 5-membered ring or a 6-membered ring. These rings may be fused with an alicyclic ring, an aromatic ring, a heterocyclic ring and an aromatic heterocyclic ring. Examples of the heterocyclic ring for the aromatic heterocyclic group include a furan ring, a pyrrole ring, a pyridine ring, a thiophene ring, an imidazole ring, an oxazole ring, a thiazole ring, a pyrazole ring, an isoxazole ring, an isothiazole ring, a pyrimidine ring, a pyrazine ring, a pyridazine ring, an indole ring, an indazole ring, a purine ring, and a quinoline ring.

The alkyl group, cycloalkyl group, aryl group and aromatic heterocyclic group for R¹ may be substituted with substituents as described above. Examples of the substituent include a halogen atom, an alkyl group, a cycloalkyl group, a bicycloalkyl group, an alkenyl group, a cycloalkenyl group, a bicycloalkenyl group, an alkynyl group, an aryl group, a heterocyclic group (preferably a 5- or 6-membered substituted or unsubstituted heterocyclic group, that is a monovalent group obtained by removing one hydrogen atom from an aromatic or non-aromatic heterocyclic compound), a cyano group, a hydroxyl group, a nitro group, a carboxyl group, an alkoxy group, an aryloxy group, a silyloxy group, a heterocyclic oxy group, an acyloxy group, a thioacyloxy group, a thioacylthio group, a carbamoyloxy group, an alkoxycarbonyloxy group, an aryloxycarbonyloxy group, an amino group (including an amino group, an alkylamino group and an anilino group), an acylamino group, an aminocarbonylamino group, an alkoxycarbonylamino group, an aryloxycarbonylamino group, a sulfamoylamino group, an alkyl- or aryl-sulfonylamino group, a mercapto group, an alkylthio group, an arylthio group, a heterocyclic thio group, a sulfamoyl group, a sulfo group, an alkyl- or aryl-sulfinyl group, an alkyl- or aryl-sulfonyl group, an acyl group, an aryloxycarbonyl group, an alkoxycarbonyl group, an aryloxythiocarbonyl group, an alkoxythiocarbonyl group, a thioacyloxy group, an (alkylthio)carbonyl group, an (arylthio)carbonyl group, an (arylthio)thiocarbonyl group, an (alkylthio)thiocarbonyl group, a thioacylthio group, a carbamoyl group, an aryl- or heterocyclic-azo group, an imido group, a phosphino group, a phosphinyl group, a phosphinyloxy group, a phosphinylamino group, and a silyl group.

Among these, preferred examples include a halogen atom, an alkyl group, a cycloalkyl group, a bicycloalkyl group, a cycloalkenyl group, a bicycloalkenyl group, an aryl group, a heterocyclic group (preferably a 5- or 6-membered substituted or unsubstituted heterocyclic group, that is a monovalent group obtained by removing one hydrogen atom from an aromatic or non-aromatic heterocyclic compound), a cyano group, a nitro group, an alkoxy group, an aryloxy group, a heterocyclic oxy group, an alkylthio group, an arylthio group, a heterocyclic thio group, an alkyl- or aryl-sulfinyl group, an alkyl- or aryl-sulfonyl group, and a silyl group.

Also, these substituents may also be further substituted. In that case, examples of the substituents include the substituents described above.

Among the substituents that may be carried by these alkyl group, cycloalkyl group, aryl group and aromatic heterocyclic group, an electron-withdrawing group is preferred, and a group having a Hammett substituent constant σ_(m) value of 0 or more is preferred. The Hammett substituent constant σ_(m) value is detailed in, for example, “Lange's Handbook of Chemistry” 12th edition by J. A. Dean, 1979 (McGraw-Hill), “Kagaku no Ryoiki” special issue, No. 122, pp. 96 to 103, 1979 (Nankodo). Among the substituents that may be carried by these alkyl group, cycloalkyl group, aryl group and aromatic heterocyclic group, more preferred examples include substituents selected from a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom), an alkoxy group (preferably having 1 to 30 carbon atoms; for example, methoxy, ethoxy, isobutoxy, n-octyloxy, or 2-ethylhexyloxy), an aryloxy group (preferably having 6 to 30 carbon atoms; for example, phenoxy or naphthoxy), an alkylthio group (preferably having 1 to 30 carbon atoms; for example, methylthio, ethylthio, n-octylthio, 2-ethylhexylthio, or n-decylthio), an arylthio group (preferably having 6 to 30 carbon atoms; for example, phenylthio or naphthylthio), an acyl group (preferably having 1 to 30 carbon atoms, including a formyl group, an alkylcarbonyl group, an arylcarbonyl group, and a heterocyclic carbonyl group; for example, formyl, acetyl, propionyl, isobutyryl, pivaloyl, acryloyl, oleoyl, benzoyl, naphthoyl, furoyl, thienoyl, or nicoinoyl), an alkoxycarbonyl group (preferably having 2 to 30 carbon atoms; for example, methoxycarbonyl, ethoxycarbonyl, benzylcarbonyl, n-octyloxycarbonyl, or 2-ethylhexylcarbonyl), and an aryloxycarbonyl group (preferably having 7 to 30 carbon atoms; for example, phenoxycarbonyl or naphthoxycarbonyl),

an acyloxy group (preferably having 1 to 30 carbon atoms, including a formyloxy group, an alkylcarbonyloxy group, an arylcarbonyloxy group, and a heterocyclic carbonyloxy group; for example, formyloxy, acetyloxy, propionyloxy, isobutyryloxy, pivaloyloxy, acryloyloxy, oleoyloxy, benzoyloxy, naphthoyloxy, furoyloxy, thienoyloxy, or nicoinoyloxy), an alkyl- or arylsulfonyl group (preferably an alkylsulfonyl group having 2 to 30 carbon atoms, or an arylsulfonyl group having 6 to 30 carbon atoms; for example, methanesulfonyl, ethanesulfonyl, n-octanesulfonyl, benzenesulfonyl, or naphthalenesulfonyl), a cyano group, an alkoxycarbonyloxy group (preferably having 2 to 30 carbon atoms; for example, methoxycarbonyloxy, ethoxycarbonyloxy, or 2-ethylhexyloxycarbonyloxy), an aryloxycarbonyloxy group (preferably having 7 to 30 carbon atoms; for example, phenoxycarbonyloxy, 4-methylphenoxycarbonyloxy, or naphthyloxycarbonyloxy), an alkoxythiocarbonyl group (preferably having 2 to 30 carbon atoms; methoxythiocarbonyl, ethoxythiocarbonyl, 2-ethylhexyloxythiocarbonyl, or n-dodecyloxythiocarbonyl), an aryloxythiocarbonyl group (preferably having 7 to 30 carbon atoms; for example, phenyloxythiocarbonyl, 3-methylphenyloxythiocarbonyl, or naphthyloxythiocarbonyl), an (alkylthio)carbonyl group (preferably having 2 to 30 carbon atoms; for example, (methylthio)carbonyl, (ethylthio)carbonyl, or (isopropylthio)carbonyl, (2-ethylhexylthio)carbonyl), an (arylthio)carbonyl group (preferably having 7 to 30 carbon atoms; (phenylthio)carbonyl or (naphthylthio)carbonyl), a thioacyloxy group (preferably having 1 to 30 carbon atoms, including a thioformyloxy group, an alkylcarbothioyloxy group, an arylcarbothioyloxy group, and a heterocyclic carbothioyloxy group; for example, thioformyloxy, thioacetyloxy, thiopropionyloxy, thioisobutyryloxy, thiopivaloyloxy, thioacryloyloxy, thiooleoyloxy, thiobenzoyloxy, thionaphthoyloxy, thiofuroyloxy, thiothienoyloxy, or thionicoinoyloxy), an (alkylthio)thiocarbonyl group (preferably having 2 to 30 carbon atoms; for example, (methylthio)thiocarbonyl, (ethylthio)thiocarbonyl, or (2-ethylhexylthio)thiocarbonyl), an (arylthio)thiocarbonyl group (preferably having 7 to 30 carbon atoms, including (phenylthio)carbonyl) or (naphthylthio)thiocarbonyl)), and a thioactylthio group (preferably having 1 to 30 carbon atoms, including a thioformylthio group, an alkylcarbothioylthio group, an arylcarbothioylthio group, and a heterocyclic carbothioylthio group; for example, thioformylthio, thioacetylthio, thiopropionylthio, thioisobutyrylthio, thiopivaloylthio, thioacryloylthio, thiooleoylthio, thiobenzoylthio, thionaphthoylthio, thiofuroylthio, thiothienoylthio, or thionicoinoylthio).

When p is 2, in the case where two R¹'s are bonded to each other and form a ring, examples of the cyclic structure include a cycloalkyl group, an aryl group, or an aromatic heterocyclic group, and in regard to these, the same groups as R¹ described above may be mentioned as examples.

In the present invention, R¹ is preferably an alkyl group, a cycloalkyl group, an aryl group or an aromatic heterocyclic group; preferably an alkyl group or an aryl group; and most preferably an alkyl group.

The structural unit represented by Formula (I) is preferably a structural unit represented by Formula (I-1), (I-2) or (I-3).

In Formula (I-1), R¹′ and R¹″ each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group or an aromatic heterocyclic group. R¹′ and R¹″ have the same meaning as R¹ in Formula (I), and preferable ranges thereof are also the same.

R¹′ and R¹″ may bond with each other to form a ring. When R¹′ and R¹″ are bonded to each other and form a ring, examples of the cyclic structure include a cycloalkyl group, an aryl group, or an aromatic heterocyclic group, and in regard to these, the same groups as R¹ described above may be mentioned as examples.

In Formula (I-2), p′ represents 0, 1 or 2; preferably 0 or 2; and more preferably 0.

Among the structural units represented by the Formulas (I-1) to (I-3), the structural unit represented by Formula (I-1) or (I-2) is preferred, and the structural unit represented by Formula (I-1) is most preferred.

The organic semiconductor polymer of the present invention is a polymer having at least the structural unit represented by Formula (I); however, the polymer may be any one of a homopolymer formed from one kind of the structural unit represented by Formula (I), a co-polymer of a combination of any of the structural units of Formulae (I-1) to (I-3), and a co-polymer with a structural unit other than the structural unit of Formula (I).

In the case of a co-polymer, regarding the structural unit other than the structural unit represented by Formula (I) of the present invention, the structural unit which can be linked each other to the structural units represented by Formula (I) by a π-electron conjugated system is used. Any structural unit may be used as long as such structural units can be conjugated by a π-electron conjugated system and the π-electron conjugated system can cover the entire polymer molecule.

Examples of the structural unit other than the structural unit represented by Formula (I) of the present invention that forms a co-polymer, include a silacyclopentadithiophene structural unit, a cyclopentadithiazole structural unit, a benzothiazole structural unit, a thiadiazoloquinoxaline structural unit, a cyclopentadithiophene structural unit, a cyclopentadithiophene oxide structural unit, a benzoisothiazole structural unit, a benzothiazole structural unit, a thiophene oxide structural unit, a thienothiophene structural unit, a thienothiophene oxide structural unit, a dithienothiophene structural unit, a dithienothiophene oxide structural unit, a tetrahydroisoindole structural unit, a fluorene structural unit, a fluorenone structural unit, an indenofluorene structural unit, a thiazole structural unit, a selenophene structural unit, a silol structural unit, a thiazolothiazole structural unit, a thienothiophene structural unit, a naphthothiadiazole structural unit, a thienopyrazine structural unit, an oxazole structural unit, an imidazole structural unit, a pyrimidine structural unit, a benzoxazole structural unit, a benzimidazole structural unit, a thienothiazole structural unit, a dithienopyrrole structural unit, a carbazole structural unit, a benzodithiophene structural unit, and a cyclopentadipyridine structural unit.

These structural units can be preferably represented by Formulas (1) to (36) or Formula (II) that will be described below.

In Formulas (1) to (36), R¹¹, R¹² and R¹⁸ each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, a heterocyclic group, an alkoxy group or an aryloxy group. R¹³ to R¹⁷ each independently represent a hydrogen atom or a substituent. Preferred examples of the substituent include a halogen atom, an alkyl group, a cycloalkyl group, an aryl group, a heterocyclic group, an alkoxy group, an aryloxy group, a cyano group, a hydroxyl group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, and an alkyl- or aryl-sulfonyl group. X² and Y¹ each independently represent CH₂, O or S. Y² represents S or Se.

The alkyl group, cycloalkyl group and aryl group for R¹¹, R¹², R¹⁸ and R¹³ to R¹⁷ have the same meanings as R¹ for Formula (I), respectively, and preferred ranges are also the same. The heterocyclic group, alkoxy group or aryloxy group for R¹¹, R¹², R¹⁸ and R¹³ to R¹⁷, and the halogen atom, acyl group, alkoxycarbonyl group, aryloxycarbonyl group, and alkyl- or arylsulfonyl group for R¹³ to R¹⁷ have the same meanings as the halogen atom, acyl group, alkoxycarbonyl group, aryloxycarbonyl group, and alkyl- or arylsulfonyl group listed as the substituents that may be carried by the alkyl group, cycloalkyl group, aryl group and aromatic heterocyclic group for R¹, respectively, and preferred ranges are also the same.

Among these, structural units represented by (1), (2), (3), (12), (14), (20), (22), (25), (27), and (35), and a structural unit represented by Formula (II) that will be described below are preferred, and structural units represented by (1), (20), and (25), and a structural unit represented by Formula (II) that will be described below are more preferred.

When the polymer having a structural unit represented by Formula (I) of the present invention is a co-polymer, a co-polymer of a structural unit represented by Formula (I) of the present invention and a structural unit represented by Formula (II) described below is particularly preferred.

In Formula (II), Z¹ and Z² each independently represent S, O, Se or Te; and Y represents C(R²¹) or N. R and R²¹ each independently represent a hydrogen atom or a substituent.

Examples of the substituents for R and R²¹ include the substituents which may be carried by the alkyl group, cycloalkyl group, aryl group and aromatic heterocyclic group for R¹.

R is preferably an alkyl group, —SO_(p)X¹, —CN, —NO₂, —P(═O)(OR²²)(OR²³) or —C(R²⁴)═C(CN)₂; and further preferably —SO_(p)X¹, —CN, —NO₂, —P(═O)(OR²²)(OR²³) or —C(R²⁴)═C(CN)₂. X¹ represents a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, an aromatic heterocyclic group or —NR²⁵(R²⁶). R²² to R²⁶ each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group or an aromatic heterocyclic group. R²⁵ and R²⁶ may bond with each other to form a ring. p represents 1 or 2.

The alkyl group, cycloalkyl group, aryl group and aromatic heterocyclic group for R²² to R²⁶ have the same meanings as the alkyl group, cycloalkyl group, aryl group and aromatic heterocyclic group for R¹, respectively, and preferred ranges are also the same.

Z¹ and Z² each are preferably S, O or Se; more preferably S or O; and most preferably S. Y is preferably CH or N; and more preferably N.

R is preferably —SO_(p)X¹. X¹ is preferably a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group or an aromatic heterocyclic group; more preferably an alkyl group, a cycloalkyl group or an aryl group; and further preferably an alkyl group or an aryl group.

p is preferably 2.

R²¹ to R²⁶ and X¹ more preferably do not contain the double bond of a vinyl group or an allyl group, an acetylene group, or the cyclic ether of an epoxy group or an oxetane group, from the viewpoint of obtaining excellent thermally stability of the polymer film thus obtained.

Specific examples of polymer having a structural unit represented by Formula (I) are shown in the followings, but the present invention is not limited thereto.

The structural unit represented by Formula (I) of the present invention can be easily synthesized by a cross-coupling reaction or the like referring to, for example, the methods described in J. Chem. Soc. Chem. Commun, p. 866 (1979) and Angew. Chem. Int. Ed. 25, p. 508 (1986) (Suzuki reaction, Yamamoto reaction, Heck reaction, Stille reaction, Sonogashira-Hagihara reaction, Kumada-Corriu reaction, Riecke reaction, and McCullogh reaction) or methods equivalent to these methods. Here, the organotin compound of the raw material can be easily synthesized by, for example, the method described in Chem. Lett. 1977, p. 301 or the like, and regarding the raw material of the co-polymer and copolymerization, synthesis can be similarly easily carried out referring to the methods described in Synthetic Communications, Vol. 11, No. 7, p. 513 (1981); Makromoleculare Chemistry, Rapid Communications, vol. 12, p. 489 (1992); and Polymer, Vol. 38, p. 1221 (1997), or methods equivalent thereto.

<Organic Semiconductor Polymer>

A polymer having the structural unit represented by Formula (I) of the present invention is useful as an organic semiconductor polymer. An organic semiconductor polymer is a polymer of an organic compound capable of exhibiting the properties as a semiconductor, and the polymer of the present invention is particularly useful as a p-type organic semiconductor polymer. Meanwhile, a p-type organic semiconductor compound, including a polymer, is generally a π-electron conjugated compound having a highest occupied molecular orbital (HOMO) energy level of 4.5 eV to 6.0 eV.

Organic semiconductor polymers are used in organic electroluminescent elements that emit light when electricity is passed, organic photoelectric conversion elements that generate power when irradiated with light, organic thin film transistor elements that control the amount of current or the amount of voltage, electrochemical sensors, printable circuits, and the like, which are used in the field of organic electronics. In the present invention, it is preferable to use organic semiconductor polymer in photovoltaic cells, and particularly in organic thin film solar cells.

<Composition for Organic Semiconductor Material>

The composition for organic semiconductor material of the present invention will be described.

The polymer having a structural unit represented by Formula (I) of the present invention is useful as a p-type organic semiconductor polymer, and the composition for organic semiconductor material of the present invention contains this polymer having a structural unit represented by Formula (I) and an n-type semiconductor compound, and particularly according to the present invention, it is preferable that the composition for organic semiconductor material contains an n-type organic semiconductor compound. Furthermore, if necessary, the composition for organic semiconductor material may contain a p-type organic semiconductor compound other than the polymer having a structural unit represented by Formula (I), and a compound other than semiconductor (for example, examples of the other p-type semiconductor compound include poly-3-hexylthiophene (P3HT), poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV), poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene](MDMO-PPV), poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazole-4,8-diyl)] (F8BT); and examples of the compound other than semiconductor include other polymers such as a polyester-based resin and a methacrylic resin that will be described below). When the mass of the composition is designated as 100, the composition contains 10 to 90 of the polymer having a structural unit represented by Formula (I), 10 to 90 of an n-type organic semiconductor compound, 0 to 50 of a p-type organic semiconductor compound other than the polymer having a structural unit represented by Formula (I), and 0 to 50 of a compound other than semiconductor.

(N-Type Organic Semiconductor Compound)

There are no particular limitations on the n-type organic semiconductor compound. Generally, the n-type organic semiconductor compound is a π-electron conjugated compound having a minimum unoccupied molecular orbital (LUMO) energy level of 3.5 eV to 4.5 eV, and examples thereof include fullerene or a derivative thereof; octaazaporphyrin; perfluoro compounds obtained by substituting the hydrogen atoms of a p-type organic semiconductor compound with fluorine atoms (for example, perfluoropentacene or perfluorophthalocyanine); and polymer compounds containing aromatic carboxylic acid anhydrides or imidation products thereof as skeletal structures, such as naphthalenetetracarboxylic acid anhydride, naphthalenetetracarboxylic acid diimide, perylenetetracarboxylic acid anhydride, and perylenetetracarboxylic acid diimide.

Among these n-type organic semiconductor compounds, fullerene or a derivative thereof is preferred, and fullerene or a derivative thereof is more preferred, so that electrical charge separation from the organic semiconductor polymer having a structural unit represented by Formula (I) of the present invention (p-type organic semiconductor compound) can be achieved rapidly and efficiently.

Examples of the fullerenes, carbon nanotubes, carbon nanohorns or a derivative thereof include fullerene C₆₀, fullerene C₇₀, fullerene C₇₆, fullerene C₇₈, fullerene C₈₄, fullerene C₂₄₀, fullerene C₅₄₀, mixed fullerene, fullerene nanotube, and a fullerene derivative a part of which is substituted with a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, alkenyl group, alkynyl group, aryl group, heteroaryl group, cycloalkyl group, silyl group, ether group, thioether group, amino group or silyl group.

As the fullerene derivative, a phenyl-C₆₁-butyric acid ester, a diphenyl-C₆₂-bis(butyric acid ester), a phenyl-C₇₁-butyric acid ester, a phenyl-C₈₅-butyric acid ester, or a thienyl-C₆₁-butyric acid ester is preferred, and the number of carbon atoms of the alcohol moiety of the butyric acid esters is preferably 1 to 30, more preferably 1 to 8, even more preferably 1 to 4, and most preferably 1.

Preferred examples of the fullerene derivative include phenyl-C₆₁-butyric acid methyl ester ([60]PCBM), phenyl-C₆₁-butyric acid n-butyl ester ([60]PCBnB), phenyl-C₆₁-butyric acid isobutyl ester ([60]PCBiB), phenyl-C₆₁-butyric acid n-hexyl ester ([60]PCBH), phenyl-C₆₁-butyric acid n-octyl ester ([60]PCBO), diphenyl-C₆₂-bis(butyric acid methyl ester)(bis[60]PCBM), phenyl-C₇₁-butyric acid methyl ester ([70]PCBM), phenyl-C₈₅-butyric acid methyl ester ([84]PCBM), thienyl-C₆₁-butyric acid methyl ester ([60]ThCBM), C₆₀ pyrrolidine tris-acid, C₆₀ pyrrolidine tris-acid ethyl ester, N-methylfulleropyrrolidine (MP-C₆₀), (1,2-methanofullerene C₆₀)-61-carboxylic acid, (1,2-methanofullerene C₆₀)-61-carboxylic acid t-butyl ester, metallocene-doped fullerene of JP-A-2008-130889 and the like, and fullerene having a cyclic ether group of U.S. Pat. No. 7,329,709 and the like.

The composition for organic semiconductor material of the present invention may contain another p-type semiconductor compound (for examples, a condensed low-molecular weight polycyclic aromatic compound, oligomer or polymer), together with the polymer having a structural unit represented by Formula (I) of the present invention.

Examples of the condensed low-molecular weight polycyclic aromatic compound as the p-type semiconductor compound include compounds such as anthracene, tetracene, pentacene, hexacene, heptacene, chrysene, pysene, fuluminene, pyrene, perpyrene, perylene, terylene, quoterylene, coronene, ovalene, circumanthracene, bisanthene, zethrene, heptazethrene, pyranthrene, violanthene, isoviolanthene, circobiphenyl, and anthradithiophene; porphyrin or copper phthaloeyanine, tetrathiafulvalene (TTF)-tetracyanoquinodimethane (TCNQ) complex, bisethylenetetrathiafulvalene (BEDTTTF)-perchloric acid complex, and derivatives or precursors thereof.

Examples of a derivative containing the condensed polycyclic compound include pentacene compounds having a substituent disclosed in WO 03/16599, WO 03/28125, U.S. Pat. No. 6,690,029 and JP-A-2004-107216; pentacene precursors disclosed in US 2003/136964; substituted acenes with a trialkylsilylethynyl group disclosed in J. Amer. Chem. Soc., vol. 127, p. 4986 (2005), J. Amer. Chem. Soc., vol. 123, p. 9482 (2001), and J. Amer. Chem. Soc., vol. 130, p. 2706 (2008); and porphyrin-series compounds disclosed in JP-A-2008-16834.

Examples of the conjugate polymer or oligomer as the p-type semiconductor compound include polymer materials such as polythiophene such as poly(3-hexylthiophene) (P3HT) and oligomer thereof; polythiophene having a polymerizable group described in Technical Digest of the International PVSEC-17, Fukuoka, Japan, 2007. p. 1225; polythiophene-thienothiophene co-polymer described in Nature Material, (2006) vol. 5, p. 328; polythiophene-diketopyrrolopyrrol co-polymer described in WO 2008/000664; polythiophene-thiazolothiazole co-polymer described in Adv. Mater, 2007, p. 4160; polythiophene co-polymer such as PCPDTBT described in Nature Mat. vol. 6 (2007), p. 497; polypyrrole and its oligomer; polyaniline, polyphenylene and its oligomer, polyphenylene vinylene and its oligomer; polythienylene vinylene and its oligomer; and δ conjugate type polymer such as polyacethylene, polydiacetylene, polysilane, and polygermane. As an oligomer material, appropriately used are oligomers such as α-sexithiophene, α,ω-dihexyl-α-sexithiophene, α,ω-dihexyl-α-quinquethiphene, α,ω-bis(3-butoxypropyl)-α-sexithiophene, all of which are thiophene hexamer.

(Photoelectric Conversion Layer)

The composition for organic semiconductor material of the present invention is preferably used as a composition for coating of a photoelectric conversion layer (particularly a bulk heterojunction layer). The mixing ratio of the p-type organic semiconductor compound which is an electron donor material, to the n-type semiconductor compound which is an electron accepting material is adjusted such that the photoelectric conversion efficiency would become the highest. Usually, the mixing ratio is selected from the range of 10:90 to 90:10, and preferably 20:80 to 80:20, as a mass ratio. Regarding the method for forming such a mixed layer, for example, a co-deposition method is used. Alternatively, the mixed layer can also formed by a coating method using a solvent which can dissolve both the organic materials. In order to increase the area of the interface at which charge separation of holes and electrons occurs, and to obtain high photoelectric conversion efficiency, a coating method is preferred.

Here, for the purpose of promoting the phase separation of the electron donating region (donor) and the electron accepting region (acceptor) in the photoelectric conversion layer, crystallization of the organic materials contained in the photoelectric conversion layer, transparentization of the electron transport layer, and the like, the photoelectric conversion layer may be subjected to a heating treatment (annealing) by various methods. In the case of a dry film forming method such as deposition, for example, there is available a method of heating the substrate temperature to 50° C. to 150° C. during film formation. In the case of a wet film forming method such as printing or coating, there is available a method of adjusting the drying temperature after coating to 50° C. to 150° C. Furthermore, the photoelectric conversion layer may also be heated to 50° C. to 150° C. in a post-process, for example, after completion of the formation of a metal negative electrode. As the phase separation is promoted, the carrier mobility increases, and high photoelectric conversion efficiency can be obtained.

<Photoelectric Conversion Element, Photovoltaic Cell>

Hereinafter, a photoelectric conversion element that uses the polymer of a structural unit represented by Formula (I) of the present invention or the composition for organic semiconductor material of the present invention, and a photovoltaic cell as a representative example of the photoelectric conversion element will be described.

In a photovoltaic cell, and particularly in an organic thin film solar cell, the composition for organic semiconductor material of the present invention is used as the photoelectric conversion layer described above, and particularly preferably as a bulk heterojunction layer.

Photovoltaic cells, and particularly the organic thin film solar cells, are generally classified into p-i-n junction type organic thin film solar cells having a p-i-n trilayer structure, and bulk heterojunction type organic thin film solar cells. In the present invention, any of them may be used, but since high photoelectric conversion efficiency is obtained easily, the present invention is particularly preferably applied to bulk heterojunction type organic thin film solar cells.

In a photovoltaic cell, the photoelectric conversion layer, and particularly the bulk heterojunction layer in a bulk heterojunction type organic thin film solar cell, is formed using the composition for organic semiconductor material of the present invention. This photoelectric conversion layer may be composed of a single layer, or may be composed of plural layers in which the kinds and mixing ratio of the p-type semiconductor compound, which is an electron donor compound, to an n-type semiconductor compound, which is an electron acceptor compound, are varied.

This photoelectric conversion layer is provided between a first electrode and a second electrode. In the present invention, it is preferable to provide a hole transport layer between the first electrode and the photoelectric conversion layer, and it is also preferable to provide an electron transport layer between the second electrode and the photoelectric conversion layer. It is particularly preferable to provide a hole transport layer between the first electrode and the photoelectric conversion layer, and to provide an electron transport layer between the photoelectric conversion layer and the second electrode.

As these hole transport layer and electron transport layer are provided, electrical charges generated at the photoelectric conversion layer can be extracted more efficiently.

(Electrode)

The photoelectric conversion element according to the present invention includes at least a first electrode and a second electrode. The first electrode and the second electrode are such that any one of them serves as a positive electrode, and the other serves as a negative electrode. Furthermore, in the case of adopting a tandem configuration, a tandem configuration can be achieved by using an intermediate electrode. Meanwhile, in the present invention, the electrode through which primarily holes flow is referred to as a positive electrode, while the electrode through which primarily electrons flow is referred to as a negative electrode. Furthermore, in view of the function of having light transmissibility or not, an electrode having light transmissibility is referred to as a transparent electrode, and an electrode having no light transmissibility is referred to as a counter electrode or a metal electrode. Usually, the positive electrode is a transparent electrode having light transmissibility, while the negative electrode is a counter electrode or a metal electrode having no light transmissibility. However, both the first electrode and the second electrode can be made into transparent electrodes.

(First Electrode)

The first electrode is a cathode. In the case using it for a solar cell, it is preferably an electrode transmitting a light of from visible light to near infrared light (380 to 800 nm). Examples of a material which can be used include transparent conductive metal oxides of indium tin oxide (ITO), SnO₂, and ZnO; a metal nanowire; and a carbon nanotubes. Further, it can be used a conductive polymer selected from the group consisting of derivatives of polypyrrole, polyaniline, polythiophene, polythienylene vinylene, polyazulene, polyisothianaphthene, polycarbazole, polyacethylene, polyphenylene, polyphenylene vinylene, polyacene, polyphenylacetylene, polydiacetylene, and polynaphthalene. Furthermore, a plural number of these electrically conductive compounds can be combined, and the combination can be used in the positive electrode. Meanwhile, in the case where light transmissibility is not required, the positive electrode may be formed using a metal material such as nickel, molybdenum, silver, tungsten, or gold. In the case where a transparent solar cell is to be produced, the transmittance of the positive electrode is preferably such that the average light transmittance at the thickness used in solar cells (for example, a thickness of 0.2 μm) in the wavelength range of 380 nm to 800 nm is preferably 75% or more, and more preferably 85% or more.

(Second Electrode)

The second electrode of the present invention is a negative electrode, and is a metal negative electrode having a standard electrode potential of a positive value.

The negative electrode may be an independent layer made of a conductive material, in addition to the material which has conductivity, it may be used a resin which holds such material together. As a conducting material used for a negative electrode, it can be used: a metal, an alloy, an electric conductive compound, and a mixture thereof, which has a small work function (4 eV or less). Specific examples of such electrode material include sodium, a sodium potassium alloy, magnesium, lithium, a magnesium/copper mixture, a magnesium/silver mixture, a magnesium/aluminum mixture, a magnesium/indium mixture, an aluminum/aluminium oxide (Al₂O₃) mixture, indium, a lithium/aluminium mixture and a rare earth metal. Among these, from the viewpoint of an electron taking out property and resistivity to oxidation, a mixture of these metals and the second metal having a larger work function than these metals is suitable. Examples of these include a magnesium/silver mixture, a magnesium/aluminum mixture, a magnesium/indium mixture, an aluminum/aluminium oxide (Al₂O₃) mixture, a lithium/aluminum mixture and aluminium. A negative electrode can be produced by using these electrode materials with a method such as a vacuum evaporation method or a sputtering method. Moreover, the coating thickness is usually chosen from the range of 10 nm to 5 μm, preferably from the range of 50 to 200 nm.

When a metallic material is used as a conducting material of the negative electrode, the light arriving at the negative electrode will be reflected and will be also reflected by the first electrode side, and this light can be reused. As a result, the light is again absorbed by the photoelectric conversion layer to result in improvement of photoelectric conversion efficiency. This is desirable. Moreover, the negative electrode may be nanoparticles, nanowires, or a nanostructure material which is made of a metal (for example, gold, silver, copper, platinum, rhodium, ruthenium, aluminium, magnesium and indium) and carbon. When it is a dispersion of nanowires, a transparent and high conductive negative electrode can be formed by a coating method, and it is preferable.

When the negative electrode side is made to be light transparent, it can be achieved as follows. After producing thin film of a conductive material suitable for negative electrodes, such as an aluminium, an aluminum alloy, silver or a silver compound to have a coating thickness of about 1 to 20 nm, a light transmitting negative electrode can be prepared by providing on the thin film with the membrane of a conductive light transparent material cited in the description of the above-mentioned positive electrode.

(Hole Transport Layer)

In the present invention, it is preferable to provide a hole transport layer between the first electrode and the photoelectric conversion layer.

Examples of the electrically conductive polymer that forms the hole transport layer include polythiophene, polypyrrole, polyaniline, polyphenylenevinylene, polyphenylene, polyacetylene, polyquinoxaline, polyoxadiazole, polybenzothiadiazole, and polymers having a plural number of these conductive skeletal structures.

Among these, polythiophene and derivatives thereof are preferred, and polyethylenedioxythiophene and polythienothiophene are particularly preferred. These polythiophenes are usually partially oxidized in order to obtain electrical conductivity. The electrical conductivity of the conductive polymer can be regulated by the degree of partial oxidation (doping amount), and as the doping amount increases, electrical conductivity increases. Since polythiophene becomes cationic as a result of partial oxidation, a counter anion for neutralizing the electrical charge is required. Examples of such a polythiophene include polyethylenedioxythiophene having polystyrene sulfonate as a counter ion (PEDOT-PSS), and polyethylenedioxythiophene having p-toluenesulfonic acid as a counter anion (PEDOT-TsO).

In the hole transport layer, another polymer may also be added thereto as long as desired electrical conductivity is not impaired. The other polymer is added for the purpose of enhancing coatability, or for the purpose of increasing the film strength. Examples of the other polymer include thermoplastic resins such as a polyester resin, a methacrylic resin, a methacrylic acid-maleic acid co-polymer, a polystyrene resin, a transparent fluororesin, a polyimide, a fluorinated polyimide resin, a polyamide resin, a polyamideimide resin, a polyether imide resin, a cellulose acylate resin, a polyurethane resin, a polyether ether ketone resin, a polycarbonate resin, an alicyclic polyolefin resin, a polyallylate resin, a polyether sulfone resin, a polysulfone resin, a cycloolefin co-polymer, a fluorene ring-modified polycarbonate resin, an alicyclic-modified polycarbonate resin, a fluorene ring-modified polyester resin, and an acryloyl compound; and hydrophilic polymers such as gelatin, polyvinyl alcohol, polyacrylic acid, polyacrylamide, polyvinylpyrrolidone, polyvinylpyridine, and polyvinylimidazole. These polymers may be crosslinked so as to increase the film strength.

Furthermore, in the hole transport layer, the cyan compounds and the like described in WO 2006/019270 can be used. In addition, to the hole transport layer which has a LUMO energy level shallower than the LUMO energy level of the n-type semiconductor compound used for a photoelectric conversion layer, there is provided an electron blocking function having a rectification effect by which the electron generated in the photoelectric conversion layer is not passed to the anode side. The above-described hole transport layer is also called an electron blocking layer, and it is more preferable to use a hole transport layer having such function. Examples of these materials include a triaryl amine compound described in JP-A-5-271166, a metal oxide such as molybdenum oxide, nickel oxide tungsten oxide and vanadium oxide. Moreover, the layer which consists of the p-type semiconductor compound used for the photoelectric conversion layer can also be used. As a means to form these layers, although any one of a vacuum deposition method and a solution coating method can be used, preferably used is a solution coating method. When a coated layer is formed as an under layer before forming a photoelectric conversion layer, it will have an effect of leveling the coating surface. This will result in decreasing a leaking effect and it is preferable.

The thickness of the hole transport layer is preferably 10 nm to 500 nm, and more preferably 20 nm to 200 nm.

(Electron Transport Layer)

In the present invention, it is preferable to provide an electron transport layer between the second electrode and the photoelectric conversion layer, and it is particularly preferable to provide a hole transport layer between the first electrode and the photoelectric conversion layer and to provide an electron transport layer between the photoelectric conversion layer and the second electrode.

Examples of the electron transporting material that can be used in the electron transport layer include the n-type semiconductor compounds described above in the photoelectric conversion layer, which are electron-acceptor materials, and the materials described as electron-transporting and hole-blocking materials in Chemical Review, Vol. 107, pp. 953-1010 (2007). In the present invention, it is preferable to use an inorganic salt or an inorganic oxide. Preferred examples of the inorganic salt include alkali metal compounds such as lithium fluoride, sodium fluoride, and cesium fluoride. Various metal oxides are preferably used as materials for electron transport layer having high stability, examples thereof include lithium oxide, magnesium oxide, aluminum oxide, calcium oxide, titanium oxide, zinc oxide, strontium oxide, niobium oxide, ruthenium oxide, indium oxide, zinc oxide, and barium oxide. Among these, relatively stable aluminum oxide, titanium oxide, and zinc oxide are more preferred. The film thickness of the electron transport layer is 0.1 nm to 500 nm, and preferably 0.5 nm to 300 nm. The electron transport layer can be suitably formed by any of a wet film forming method based on coating or the like, a dry film forming method according to a PVD method such as deposition or sputtering, a transfer method, a printing method, and the like.

Meanwhile, the electron transport layer that has a HOMO energy level that is deeper than the HOMO energy level of the p-type semiconductor compound used in the photoelectric conversion layer, is imparted with a hole blocking function of having a rectification effect in which holes produced in the photoelectric conversion layer are not passed to the negative electrode side. More preferably, the material having the HOMO energy level deeper than the HOMO energy level of the n-type semiconductor compound is used as the electron transport layer. Further, in view of the characteristics of transporting electrons, it is preferable to use a compound having high electron mobility. Such an electron transport layer is also called a hole blocking layer, and it is preferable to use an electron transport layer having such a function. As such a material, phenanthrene-based compounds such as bathocuproine; n-type semiconductor compounds such as naphthalenetetracarboxylic acid anhydride, naphthalenetetracarboxylic acid diimide, perylenetetracarboxylic acid anhydride, and perylenetetracarboxylic acid diimide; n-type inorganic oxides such as titanium oxide, zinc oxide, and gallium oxide; and alkali metal compounds such as lithium fluoride, sodium fluoride, and cesium fluoride, can be used. Furthermore, a layer formed from a simple substance of the n-type semiconductor compound used in the photoelectric conversion layer can also be used.

(Support)

The support that constitutes the photovoltaic cell of the present invention is not particularly limited as long as at least a first electrode (positive electrode), a photoelectric conversion layer, and a second electrode (metal negative electrode), and in a more preferred embodiment, a first electrode (positive electrode), a hole transport layer, a photoelectric conversion layer, an electron transport layer, and a second electrode (metal negative electrode), can be formed on the support and retained thereon. For example, the support can be appropriately selected from a glass plate, a plastic film and the like according to the purpose.

Hereinafter, a plastic film substrate as a representative example of the support will be described.

The material, thickness and the like of the plastic film substrate are not particularly limited and can be appropriately selected according to the purpose. In the case of producing an organic thin film solar cell having light transmissibility, a plastic film substrate having excellent transmissibility to light, for example, light having a wavelength in the range of 400 nm to 800 nm, is preferred.

Light transmittance can be calculated by measuring the total light transmittance and the amount of scattered light using the method described in JIS K7105, that is, using an integrating sphere type light transmittance measuring apparatus, and subtracting the diffuse transmittance from the total light transmittance.

As the material of the plastic film that can be used for the support, specific examples include thermoplastic resins, such as polyester resins, methacryl resins, methacrylic acid-maleic anhydride co-polymers, polystyrene resins, transparent fluororesins, polyimides, fluoropolyimide resins, polyamide resins, polyamidimide resins, polyetherimide resins, cellulose acylate resins, polyurethane resins, polyether ether ketone resins, polycarbonate resins, alicyclic polyolefin resins, polyarylate resins, polyether sulfone resins, polysulfone resins, cycloolefin co-polymers, fluorene ring-modified polycarbonate resins, alicyclic-modified polycarbonate resins, fluorene ring-modified polyester resins, and acryloyl compounds.

It is preferable that the plastic film substrate be formed from a material having heat resistance. Specifically, it is preferable that the plastic film substrate be formed from a material which has heat resistance that satisfies at least any one property of a glass transition temperature (Tg) of 100° C. or more and a linear thermal expansion coefficient of 40 ppm·K⁻¹ or less, and also has high transparency to the wavelength of the exposure light as described above.

Meanwhile, the Tg and linear expansion coefficient of a plastic film are measured by the method for measuring the transition temperature of a plastic as described in JIS K7121, and the method for testing the linear expansion coefficient by a thermomechanical analysis for a plastic as described in JIS K7197, and in the present invention, the values measured by this method are used.

Tg and the linear expansion coefficient of the plastic film substrate may be controlled by an additive or the like. Examples of such a thermoplastic resin excellent in heat resistance includes polyethylene naphthalate (PEN: 120° C.), polycarbonate (PC: 140° C.), alicyclicpolyolefin (e.g., Nippon Zeon's Zeonoa 1600: 160° C.), polyarylate (PAr: 210° C.), polyether sulfone (PES: 220° C.), polysulfone (PSF: 190° C.), cycloolefin co-polymer (COC, compound described in JP-A 2001-150584: 162° C.), fluorene ring-modified polycarbonate (BCF-PC, compound described in JP-A 2000-227603: 225° C.), alicyclic-modified polycarbonate (IP-PC, compound described in JP-A 2000-227603: 205° C.), acryloyl compounds (compounds described in JP-A 2002-80616: 300° C. or more), and polyimide (the parenthesized data are Tg). These are suitable as the base material according to the present invention. In particular, for high transparency, use of alicyclic polyolefin is preferred.

The plastic film that is used as the support is required to be transparent to light. More specifically, the light transmittance to light having a wavelength in the range of 400 nm to 800 nm is usually preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

There are no particular limitations on the thickness of the plastic film, the thickness is typically 1 μm to 800 μm, and preferably 10 μm to 300 μm.

On the back surface side (surface on the side where a positive electrode is not formed) of the plastic film, a functional layer which is publicly known may be provided. Examples thereof include a gas barrier layer, a matting agent layer, a reflection preventive layer, a hard coat layer, an anti-fog layer, and an anti-fouling layer. In addition to these, functional layers are described in detail in paragraphs [0036] to [0038] of JP-A-2006-289627.

(Easily Adhesive Layer/Undercoat Layer)

The front surface (surface on the side where a positive electrode is formed) of the plastic film may have an easily adhesive layer or an undercoat layer from the viewpoint of enhancing adhesiveness. The easily adhesive layer or undercoat layer may be a single layer, or may be a multilayer.

For the formation of the easily adhesive layer or undercoat layer, various hydrophilic primer coating polymers are used. Examples of the hydrophilic primer coating polymers that are used in the present invention include water-soluble polymers such as gelatin, gelatin derivatives, casein, agar, sodium alginate, starch, and polyvinyl alcohol; cellulose esters such as carboxymethyl cellulose and hydroxyethyl cellulose; latex polymers such as vinyl chloride-containing co-polymers, vinylidene chloride-containing co-polymers, acrylic acid ester-containing co-polymers, vinyl acetate-containing co-polymers, and butadiene-containing co-polymers; polyacrylic acid co-polymers, and maleic anhydride co-polymers.

The coating film thickness after drying of the easily adhesive layer or undercoat layer is preferably in the range of 50 nm to 2 μm. Also, in the case of using the support as a provisional support, the support surface can be subjected to a treatment for easy detachability.

(Functional Layer)

On the back surface side (surface on the side where a positive electrode is not formed) of the support, a functional layer may be provided. Examples thereof include a gas barrier layer, a matting agent layer, a reflection preventive layer, a hard coat layer, an anti-fog layer, an anti-fouling layer, and an easily adhesive layer. In addition to these, functional layers are described in detail in paragraphs [0036] to [0038] of JP-A-2006-289627, and the functional layers described therein may be provided in accordance with the purpose.

<Recombination Layer>

The solar cell according to the present invention may have a so-called tandem type configuration in which plural photoelectric conversion layers are laminated. The tandem type configuration may be of series connection type or parallel connection type.

In a tandem type element having two photoelectric conversion layers, a recombination layer is provided between the two photoelectric conversion layers. As the material for the recombination layer, an ultrathin film of an electrically conductive material is used. Preferred examples of the conductive material include gold, silver, aluminum, platinum, titanium oxide, and ruthenium oxide. Among these, silver that is relatively inexpensive and stable is preferred. The film thickness of the recombination layer is 0.01 nm to 5 nm, preferably 0.1 nm to 1 nm, and particularly preferably 0.2 nm to 0.6 nm. There are no particular limitations on the method for forming the recombination layer, and the recombination layer can be formed by, for example, a PVD method such as a vacuum deposition method, a sputtering method, or an ion plating method.

<Other Semiconductor Layers>

If necessary, the photovoltaic cell may also include auxiliary layers such as a hole inhibiting layer and an exciton diffusion prevention layer. Meanwhile, in the present invention, the photovoltaic cell may include layers such as a photoelectric conversion layer, a hole transport layer, a hole injection layer, an electron transport layer, an electron injection layer, an electron inhibiting layer, a hole inhibiting layer, and an exciton diffusion prevention layer, which are formed between the first electrode and the second electrode (the positive electrode and the metal negative electrode). The layers which transport electrons or holes will be collectively referred to as “semiconductor layers”.

<Protective Layer>

The photovoltaic cell according to the present invention may be coated with a protective layer. Examples of the material that is contained in the protective layer include inorganic materials, including metal oxides such as magnesium oxide, aluminum oxide, silicon oxide (SiOx), titanium oxide, germanium oxide, yttrium oxide, zirconium oxide, and hafnium oxide; metal nitrides such as silicon nitride (SiNx); metal nitride oxides (metal oxynitrides) such as silicon nitride oxide (SiOxNy); metal fluorides such as lithium fluoride, magnesium fluoride, aluminum fluoride, and calcium fluoride; and diamond-like carbon (DLC). Examples of organic materials include polymers such as polyethylene, polypropylene, polyvinylidene fluoride, polyparaxylylene, and polyvinyl alcohol. Among these, oxides, nitrides and nitride oxides of metals, and DLC are preferred, and oxides, nitrides and nitride oxides of silicon and aluminum are particularly preferred. The protective layer may have a configuration of a single layer or a multilayer.

There are no particular limitations on the method for forming the protective layer, and for example, PVD methods such as a vacuum deposition method, a sputtering method, an MBE (molecular beam epitaxy) method, a cluster ion beam method, an ion plating method, and a plasma polymerization method; various CVD methods including an atomic layer deposition method (ALD method or ALE method), coating methods, printing methods, and transfer methods can be applied. In the present invention, the protective layer may be used as a conductive layer.

<Gas Barrier Layer>

A protective layer that is intended to inhibit the penetration of active factors such as water molecules or oxygen molecules is also particularly referred to as a gas barrier layer, and the photovoltaic cell, particularly organic thin film solar cell, according to the present invention preferably has a gas barrier layer. The gas barrier layer is not particularly limited as long as it is a layer which blocks active factors such as water molecules or oxygen molecules, and those materials previously exemplified for the protective layer are usually used. These may be pure materials, or may be mixtures having plural compositions, or graded compositions. Among these, oxides, nitrides, and nitride oxides of silicon and aluminum are preferred.

The gas barrier layer may be a single layer, or may include plural layers. For the gas barrier layer, a laminate of an organic material layer and an inorganic material layer may be used, or an alternating laminate of plural inorganic material layers and plural organic material layers may also be used. The organic material layer is not particularly limited as long as the layer is smooth, but preferred examples include layers formed from polymerization products of (meth)acrylates. Regarding the inorganic material layer, the materials for the protective layer described above are preferred, and oxides, nitrides, and nitride oxides of silicon and aluminum are particularly preferred.

Not specifically defined, the thickness of the inorganic material layer is generally within a range of from 5 to 500 nm per one layer, preferably from 10 to 200 nm per one layer. The inorganic material layer may be a laminate composed of a plurality of sub-layers. In this case, each sub-layer may have the same composition, or a different composition. In addition, as so mentioned hereinabove and as disclosed in US 2004/00046497, the inorganic layers may be gradation layers of which the composition changes continuously in the thickness direction of the layer, with no definite boundary to the adjacent inorganic layer.

The thickness of the photovoltaic cell according to the present invention is not particularly limited. In the case of producing an organic thin film solar cell having light transmissibility, the thickness is preferably 50 μm to 1 mm, and more preferably 100 μm to 500 μm.

When a module for sunlight power generation is produced using the photovoltaic cell according to the present invention, reference can be made to the descriptions in Yoshihiro Hamakawa, “Taiyoko Hatsuden: Saishin no Gijutsu to Shisutemu (Photovoltaic power generation: Latest Technologies and Systems)”, CMC Publishing (2000), and the like.

The polymer having a structural unit represented by Formula (I) of the present invention, and the photovoltaic cell have been described, and in some embodiments, the polymer having a structural unit represented by Formula (I) of the present invention can be used in other elements and systems. For example, such a polymer can be used in suitable organic semiconductor elements such as field effect transistors, photodetectors (for example, infrared light detectors), photovoltaic detectors, image pickup elements (for example, RGB image pickup elements of cameras or medical image pickup systems), light emitting diodes (LED) (for example, organic LED's or infrared or near-infrared LED's), laser elements, conversion layers (for example, layers that convert visible light emission to infrared light emission), amplifier radiators for electric communication (for example, doping agent for fibers), memory elements (for example, holographic memory elements), and electrochromic elements (for example, electrochromic displays).

EXAMPLES

The present invention will be described in more detail based on the following examples. The materials, used amounts, proportions, treatments, treatment procedures and the like indicated in the following Examples can be appropriately modified as long as the purport of the present invention is maintained. It is therefore understood that the present invention is by no means intended to be limited to the specific examples below.

Example 1 Synthesis of Polymer 1

Compound 1-C was synthesized according to the following scheme, and polymer 1 was synthesized from this compound 1-C.

In a nitrogen atmosphere, 3.2 g of compound (1-A) (synthesized by the synthesis method for Compound 5 described in Organic Letters, Vol. 12, p. 5478-5481 (2010)) was dissolved in 50 mL of dry tetrahydrofuran (THF), and the solution was cooled to an internal temperature of −80° C. or lower. 6.9 mL of n-butyllithium (1.6 mol/L hexane solution) was added dropwise thereto at an internal temperature of −80° C. or lower, and the mixture was stirred for 30 minutes. 1.39 mL of dichlorodihexylsilane was added dropwise thereto at an internal temperature of −80° C. or lower, and the mixture was maintained for one hour at this temperature. Subsequently, the temperature was slowly increased to room temperature. After 12 hours, 50 mL of a saturated aqueous solution of sodium hydrogen carbonate and 50 mL of ethyl acetate were added to the mixture, and the resulting mixture was left to stand to remove an aqueous layer. The organic layer was washed with water and saturated brine, and was dried over anhydrous magnesium sulfate, and then the solvent was distilled off. The residue thus obtained was purified by silica gel column chromatography, and compound (1-B) was obtained. Yield amount: 1.6 g (yield: 47%).

1.35 g of compound (1-B) was dissolved in 27 mL of dry THF, and 0.73 g of N-bromosuccinimide was added thereto. A reaction liquid thus obtained was allowed to react for 4 hours at room temperature. The solvent was distilled off under reduced pressure, and the residue was purified by silica gel column chromatography. Thus, compound (1-C) was obtained. Yield amount: 0.94 g (yield: 90%).

In a nitrogen atmosphere, 0.44 g of bis(1,5-cyclooctadiene)nickel(0), 0.75 mL of 1,5-cyclooctadiene, and 0.27 g of 2,2′-bipyridyl were suspended in 10 mL of N,N-dimethylformamide (DMF), and a solution prepared by dissolving 0.71 g of compound (1-C) in 5 mL of DMF was added dropwise to this suspension. The mixture was stirred for 24 hours at 60° C. A reaction liquid obtained was added dropwise to a mixed liquid of 5 mL of 2 mol/L hydrochloric acid and 10 mL of methanol, and a solid thus obtained was washed with 2 mol/L hydrochloric acid, an aqueous solution of disodium ethylenediamine tetraacetate, an aqueous solution of sodium diethyldithiocarbamate, and methanol. Subsequently, the solid was transferred to a Soxhlet extractor and washed with acetone. The solid thus obtained was dried under reduced pressure, and thus a polymer 1 was obtained. Yield amount: 0.47 g.

The polymer 1 was subjected to an analysis of molecular weight by GPC, and the weight average molecular weight (Mw) calculated relative to standard polystyrenes was 22,000. The ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) was 1.45. Furthermore, the polymer 1 was dissolved in chlorobenzene, and the solution was applied on a glass substrate by spin coating. The absorption spectrum of the coating film was measured, and it was found that λmax was 670 nm. Meanwhile, measurement of the absorption spectrum was carried out using a spectrophotometer (Model UV-3600 manufactured by Shimadzu Corp.).

Example 2 Synthesis of Polymer 2

Compound 2-C was synthesized according to the following scheme, and polymer 2 was synthesized from this compound 2-C.

Compound (2-B) was synthesized in the same manner as in Example 1, except that 1.39 mL of dichlorodihexylsilane was changed to 1.63 g of dichlorodi(2-ethylhexyl)silane. 1.6 g (yield: 47%). Also, dichlorodi(2-ethylhexyl)silane was synthesized according to the synthesis method for Compound 2 described in Journal of the American Chemical Society, Vol. 130, pp. 16144-16145 (2008).

Compound (2-C) was synthesized in the same manner as in Example 1, except that 1.35 g of compound (1-B) was changed to 1.46 g of compound (2-B). Yield amount: 1.1 g (yield: 95%).

Polymer 2 was synthesized in the same manner as in Example 1, except that 0.71 g of compound (1-C) was changed to 0.79 g of compound (2-C). Yield amount: 0.50 g.

The polymer 2 was subjected to an analysis of molecular weight by GPC, and the weight average molecular weight (Mw) calculated relative to standard polystyrenes was 21,000. The ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) was 1.53. Similarly, the absorption spectrum of the coating film of polymer 2 was measured, and it was found that λmax was 680 nm.

Example 3 Synthesis of Polymer 3

Compound 3-E was synthesized according to the following scheme, and polymer 3 was synthesized from this compound 3-E.

Compound (3-B) was synthesized using compound (3-A) according to the method described in Justus Liebigs Annalen der Chemie, Vol. 512, p. 136-156 (1934). Compound (3-C) was synthesized by making reference to the method described in Journal of Heterocyclic Chemistry, Vol. 20, p. 113-119 (1983). Compound (3-D) was synthesized by making reference to the method described in Journal of Heterocyclic Chemistry, Vol. 20, p. 113-119 (1983). Compound (3-E) was synthesized by making reference to the method described in Bioscience, Biotechnology, Biochemistry, Vol. 57, 1561-1562 (1993).

Polymer 3 was synthesized in the same manner as in Example 1, except that 0.71 g of compound (1-C) was changed to 0.48 g of compound (3-E). Yield amount: 0.24 g.

The polymer 3 was subjected to an analysis of molecular weight by GPC, and the weight average molecular weight (Mw) calculated relative to standard polystyrenes was 17,000. The ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) was 1.51. Similarly, the absorption spectrum of the coating film of polymer 3 was measured, and it was found that λmax was 630 nm.

Example 4 Synthesis of Polymer 4

According to the following scheme, polymer 4 was synthesized from this compound 4-A.

Compound (4-A) was synthesized using compound (3-E) by making reference to the method described in Tetrahedron Letters, Vol. 47, 2009-2012 (2006).

Polymer 4 was synthesized in the same manner as in Example 1, except that 0.71 g of compound (1-C) was changed to 0.51 g of compound (4-A). Yield amount: 0.26 g.

The polymer 4 was subjected to an analysis of molecular weight by GPC, and the weight average molecular weight (Mw) calculated relative to standard polystyrenes was 18,500. The ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) was 1.47. Similarly, the absorption spectrum of the coating film of polymer 4 was measured, and it was found that λmax was 630 nm.

Example 5 Synthesis of Polymer 5

According to the following scheme, polymer 5 was synthesized from this compound 5-A.

Compound (5-A) was synthesized using compound (3-E) by making reference to the method described in Tetrahedron Letters, Vol. 47, 2009-2012 (2006).

Polymer 5 was synthesized in the same manner as in Example 1, except that 0.71 g of compound (1-C) was changed to 0.53 g of compound (5-A). Yield amount: 0.29 g.

The polymer 5 was subjected to an analysis of molecular weight by GPC, and the weight average molecular weight (Mw) calculated relative to standard polystyrenes was 17,300. The ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) was 1.43. Similarly, the absorption spectrum of the coating film of polymer 5 was measured, and it was found that λmax was 620 nm.

Example 6 Synthesis of Polymer 6

According to the following scheme, polymer 6 was synthesized from this compound 6-D.

Compound (6-B) was synthesized using compound (6-A) according to the method described in Journal of Organic Chemistry, Vol. 62, p. 4088-4096 (1997). Compound (6-C) was synthesized by making reference to the methods described in Helvetica Chimica Acta, Vol. 85, p. 4485-4517 (2002) and Collection of Czachoslovak ChemicalCommunications, Vol. 51, p. 1678-1684 (1986). Compound (6-D) was synthesized by making reference to the method described in Bioscience, Biotechnology, Biochemistry, 1993, Vol. 57, p. 1561-1562.

Polymer 6 was synthesized in the same manner as in Example 1, except that 0.71 g of compound (1-C) was changed to 0.46 g of compound (6-D). Yield amount: 0.23 g.

The polymer 6 was subjected to an analysis of molecular weight by GPC, and the weight average molecular weight (Mw) calculated relative to standard polystyrenes was 16,500. The ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) was 1.54. Similarly, the absorption spectrum of the coating film of polymer 2 was measured, and it was found that λmax was 710 nm.

Example 7 Synthesis of Polymer 7

Polymer 7 was synthesized as follow.

0.12 g of compound (1-C), 0.15 g of compound (7-A) (synthesized by the method described in Example 1 of WO 2008/067023), 2.1 mg of tris(dibenzylideneacetone)dipalladium(0), 4.2 mg of triphenylphosphine, and 35 mg of Aliquat 336 were dissolved in 20 mL of toluene and 15 mL of THF, and 2 mL of a 2 mol/L aqueous solution of sodium carbonate was added thereto. The solution was degassed and then purged with nitrogen, and the solution was allowed to react for 48 hours at 90° C. The reaction liquid thus obtained was cooled to room temperature, and the solvent was distilled off under reduced pressure. The residue thus obtained was washed with methanol, and was washed with acetone. A solid thus obtained was dissolved in chloroform, the solution was filtered through a 0.45-μm filter, and the solvent was distilled off under reduced pressure. A solid thus obtained was dissolved in toluene, and the solution was mixed with an aqueous solution of sodium diethyldithiocarbamate. The mixture was stirred for 12 hours at 80° C. in a nitrogen atmosphere. After the mixture was left to stand, the aqueous layer was removed, ion exchanged water was added to the organic layer, and the resulting mixture was stirred. After the mixture was left to stand, the aqueous solution was removed, and the organic layer was recovered. The organic layer was dried over anhydrous magnesium sulfate, and then the solvent was distilled off under reduced pressure. A solid thus obtained was transferred into a Soxhlet extractor, and the solid was extracted with methanol for 12 hours and further extracted with acetone for 12 hours. The solid was dried under reduced pressure, and thus polymer 7 was obtained. Yield amount: 0.16 g.

The polymer 7 was subjected to an analysis of molecular weight by GPC, and the weight average molecular weight (Mw) calculated relative to standard polystyrenes was 19,100. The ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) was 1.42. Similarly, the absorption spectrum of the coating film of polymer 7 was measured, and it was found that λmax was 640 nm.

Example 8 Synthesis of Polymer 8

Polymer 8 was synthesized as follow.

Polymer 8 was synthesized in the same manner as in Example 7, except that 0.15 g of compound (7-A) was changed to 0.08 g of compound (8-A) (synthesized by the method described in Example 17 of WO 2003/074533). Yield amount: 0.10 g.

The polymer 8 was subjected to an analysis of molecular weight by GPC, and the weight average molecular weight (Mw) calculated relative to standard polystyrenes was 23,100. The ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) was 1.45. Similarly, the absorption spectrum of the coating film of polymer 8 was measured, and it was found that λmax was 630 nm.

Example 9 Synthesis of Polymer 9

Polymer 9 was synthesized as follow.

0.26 g of compound (1-C) and 0.35 g of compound (9-A) (synthesized by the method described in Example 1 of JP-T-2010-507233) were dissolved in 12 mL of dehydrated toluene, and 12.55 mg of tris(dibenzylideneacetone)dipalladium(0) and 28.80 mg of triphenylphosphine were added. The solution was degassed and then purged with nitrogen, and was allowed to react for 48 hours at 120° C. The reaction liquid thus obtained was cooled to room temperature, and the solvent was distilled off under reduced pressure. The residue thus obtained was washed with methanol, and was washed with acetone. A solid thus obtained was dissolved in chloroform, the solution was filtered through a 0.45-μm filter, and the solvent was distilled off under reduced pressure. A solid thus obtained was dissolved in toluene, the solution was mixed with an aqueous solution of sodium diethyldithiocarbamate, and the mixture was stirred for 12 hours at 80° C. in a nitrogen atmosphere. After the mixture was left to stand, the aqueous layer was removed, ion exchanged water was added to the organic layer, and the resulting mixture was stirred. After the mixture was left to stand, the aqueous solution was removed, and the organic layer was recovered. The organic layer was dried over anhydrous magnesium sulfate, and then the solvent was distilled off under reduced pressure. A solid thus obtained was transferred into a Soxhlet extractor, and the solid was extracted with methanol for 12 hours and extracted with acetone for 12 hours. The solid was dried under reduced pressure, and thus polymer 9 was obtained. Yield amount: 0.34 g.

The polymer 9 was subjected to an analysis of molecular weight by GPC, and the weight average molecular weight (Mw) calculated relative to standard polystyrenes was 19,700. The ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) was 1.48. Similarly, the absorption spectrum of the coating film of polymer 9 was measured, and it was found that λmax was 620 nm.

Example 10 Synthesis of Polymer 10

Polymer 10 was synthesized as follow.

Polymer 10 was synthesized in the same manner as in Example 9, except that 0.35 g of compound (9-A) was changed to 0.26 g of compound (10-A) (synthesized by the method described on page 14 of WO 2010/062948). Yield amount: 0.26 g.

The polymer 10 was subjected to an analysis of molecular weight by GPC, and the weight average molecular weight (Mw) calculated relative to standard polystyrenes was 18,600. The ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) was 1.39. Similarly, the absorption spectrum of the coating film of polymer 10 was measured, and it was found that λmax was 510 nm.

Example 11 Synthesis of Polymer 11

Synthesis of monomer 11-13 was carried out in the same manner as in Scheme 1 described below, and polymer 11 was synthesized from this monomer 11-13.

(Synthesis of Intermediate 11-2)

111.3 g of Compound 1 and 38.1 g of thiourea were added to 250 ml of ethanol, and the mixture was heated to reflux for 2 hours. The reaction liquid was poured into ice water, and a 10% aqueous solution of sodium hydroxide was added thereto until the reaction liquid turned weakly alkaline. The mixture was extracted with ethyl acetate. The extract was washed with a saturated aqueous solution of sodium hydrogen carbonate and saturated brine, and then was dried over anhydrous magnesium sulfate. After filtration, the solvent was distilled off under reduced pressure, and the residue was crystallized from an ethyl acetate/hexane mixed solvent. Thus, 100.2 g of an intermediate 11-2 was obtained. Yield: 82.0%.

(Synthesis of Intermediate 11-3)

56.5 g of copper (II) chloride was added to 1 L of acetonitrile, and 44.5 g of isoamyl nitrite was added thereto at room temperature. The temperature was increased to 30° C., and then 92.8 g of the intermediate 11-2 was added thereto over one hour at 30° C. to 32° C. The temperature was increased to 40° C., and the mixture was allowed to react for 2 hours. Subsequently, the reaction mixture was poured into water, and ethyl acetate was added thereto. The mixture was filtered through Celite, and then the filtrate was subjected to liquid-liquid partition. The organic layer was washed with an aqueous solution of sodium sulfite and saturated brine, and then was dried over anhydrous magnesium sulfate. After filtration, the solvent was distilled under reduced pressure, and the residue was purified by silica gel column chromatography. Thus, 71.8 g of an intermediate 11-3 was obtained. Yield: 71.7%.

(Synthesis of Intermediate 11-4)

Under water cooling, 22.1 g of the intermediate 11-3, 12.3 g of n-octanethiol, and 23.1 g of potassium carbonate were added to 250 ml of acetone, and the mixture was allowed to react for 6 hours at room temperature. The reaction mixture was poured into ice water, and ethyl acetate and 5 ml of an aqueous solution of sodium hypochlorite were added thereto. The mixture was subjected to liquid-liquid partition, and the organic layer was washed with saturated brine, and then was dried over anhydrous magnesium sulfate. After filtration, the solvent was distilled off under reduced pressure, and thus 30.6 g of an intermediate 11-4 was obtained. Yield: 97.7%.

(Synthesis of Intermediate 11-5)

4.56 g of lithium aluminum hydride was added to 300 ml of dry THF, and while the mixture was cooled with an ice-acetone coolant, a solution prepared by dissolving 29.9 g of the intermediate 11-4 in 100 ml of dry THF was added dropwise thereto over 45 minutes at or below 5° C. The mixture was allowed to react for 15 minutes at or below 5° C., and then 50 ml of acetone was added dropwise thereto over 5 minutes at or below 17° C. The mixture was stirred for 10 minutes at room temperature, and then 50 ml of 1 N aqueous hydrochloric acid was added dropwise thereto over 15 minutes under water cooling. The mixture was stirred for 30 minutes at room temperature, and then ethyl acetate and hexane were added thereto. The mixture was filtered through Celite, and then the filtrate was subjected to liquid-liquid partition. The organic layer was washed with water, a saturated aqueous solution of sodium hydrogen carbonate, and saturated brine, and then was dried over anhydrous magnesium sulfate. After filtration, the solvent was distilled off under reduced pressure, and the residue was purified by silica gel column chromatography. Thus, 19.1 g of an intermediate 11-5 was obtained. Yield: 82.3%.

(Synthesis of Intermediate 11-6)

17.4 g of the intermediate 11-5 and 1.5 ml of pyridine were added to 200 ml of toluene, and while the mixture was cooled with an ice-acetone coolant, a solution prepared by dissolving 13.1 ml of thionyl chloride in 100 ml of toluene was added dropwise to the mixture over 25 minutes at or below 4° C. The mixture was allowed to react for one hour at or below 7° C., and then the reaction mixture was poured into ice water. The mixture was extracted with ethyl acetate. The mixture was subjected to liquid-liquid partition, and the organic layer was washed with a saturated aqueous solution of sodium hydrogen carbonate and saturated brine, and then was dried over anhydrous magnesium sulfate. After filtration, the solvent was distilled off under reduced pressure, and thus 18.2 g of an intermediate 11-6 was obtained. Yield: 92.8%.

(Synthesis of Intermediate 11-7)

16.3 g of the intermediate 11-6 and 50 ml of 1 N aqueous hydrochloric acid were added to 200 ml of acetone, and the mixture was heated to reflux for 3 hours. Furthermore, 20 ml of 1 N aqueous hydrochloric acid was added to the mixture, and the resulting mixture was heated to reflux for 5.5 hours. The mixture was extracted with ethyl acetate, and the organic layer was washed with a saturated aqueous solution of sodium hydrogen carbonate and saturated brine, and then was dried over anhydrous magnesium sulfate. After filtration, the solvent was distilled off under reduced pressure, and thus 15.4 g of an intermediate 11-7 was obtained. Yield: 100%.

(Synthesis of Intermediate 11-8)

15.1 g of the intermediate 11-7 and 6.3 g of sodium thioacetate were added to 200 ml of acetone, and the mixture was stirred for one hour at room temperature. The mixture was poured into water, and the mixture was extracted with ethyl acetate. The mixture was subjected to liquid-liquid partition, and the organic layer was washed with a saturated aqueous solution of sodium hydrogen carbonate and saturated brine, and then was dried over anhydrous magnesium sulfate. After filtration, the solvent was distilled off under reduced pressure, and the residue was purified by silica gel column chromatography. Thus, 14.9 g of an intermediate 11-8 was obtained. Yield: 87.5%.

(Synthesis of Intermediate 11-9)

13.9 g of the intermediate 11-8 and 1.0 ml of pyridine were added to 150 ml of toluene, and while the mixture was cooled with an ice-acetone coolant, a solution prepared by dissolving 4.4 ml of thionyl chloride in 50 ml of toluene was added dropwise to the mixture over 30 minutes at or below 5° C. The mixture was allowed to react for one hour at or below 5° C., and then the reaction mixture was poured into ice water. The mixture was extracted with ethyl acetate. The mixture was subjected to liquid-liquid partition, and the organic layer was washed with a saturated aqueous solution of sodium hydrogen carbonate and saturated brine, and then was dried over anhydrous magnesium sulfate. After filtration, the solvent was distilled off under reduced pressure, and thus 14.1 g of an intermediate 11-9 was obtained. Yield: 96.5%.

(Synthesis of Intermediate 11-10)

13.2 g of the intermediate 11-9 was added to 200 ml of acetone, and while the mixture was cooled with an ice-acetone coolant, 7.4 ml of a 28% sodium methoxide methanol solution was added dropwise thereto over 10 minutes at or below 0° C. under nitrogen stream. The mixture was stirred for 30 minutes at or below 5° C., and then was poured into water. The resulting mixture was extracted with ethyl acetate. The resulting mixture was subjected to liquid-liquid partition, and the organic layer was washed with a saturated aqueous solution of sodium hydrogen carbonate and saturated brine, and then was dried over anhydrous magnesium sulfate. After filtration, the solvent was distilled off under reduced pressure, and the residue was purified by silica gel column chromatography. Thus, 8.53 g of an intermediate 11-10 was obtained.

Yield: 82.3%.

(Synthesis of Intermediate 11-11)

8.04 g of the intermediate 11-10 was added to 100 ml of toluene, and 6.81 g of DDQ was added thereto over 10 minutes at room temperature. The mixture was heated to reflux for 2 hours, and then was poured into ice water. The mixture was extracted with ethyl acetate. The mixture was subjected to liquid-liquid partition, and the organic layer was washed with an aqueous solution of sodium sulfite, a saturated aqueous solution of sodium hydrogen carbonate, and saturated brine, and then was dried over anhydrous magnesium sulfate. After filtration, the solvent was distilled off under reduced pressure, and the residue was purified by silica gel column chromatography. Thus, 6.56 g of an intermediate 11-11 was obtained. Yield: 82.2%.

(Synthesis of Intermediate 11-12)

5.75 g of the intermediate 11-11 was added to 100 ml of chloroform, and 7.59 g of m-CPBA was added thereto over 30 minutes under ice cooling. The temperature was increased to room temperature, and the mixture was stirred for 3 hours. The mixture was poured into ice water, and was extracted with chloroform. The mixture was subjected to liquid-liquid partition, and the organic layer was washed with an aqueous solution of sodium sulfite, a saturated aqueous solution of sodium hydrogen carbonate, and saturated brine, and then was dried over anhydrous magnesium sulfate. After filtration, the solvent was distilled off under reduced pressure, and the residue was purified by silica gel column chromatography. Thus, 4.87 g of an intermediate 11-12 was obtained. Yield: 76.7%.

(Synthesis of Intermediate 11-13)

4.76 g of the intermediate 11-12 was added to 100 ml of chloroform, and 5.87 g of N-bromosuccinimide was added thereto over 30 minutes under ice cooling. The temperature was increased to room temperature, and the mixture was stirred for one hour. Subsequently, the mixture was poured into ice water, and the resulting mixture was extracted with chloroform. The resulting mixture was subjected to liquid-liquid partition, and the organic layer was washed with a saturated aqueous solution of sodium hydrogen carbonate and saturated brine, and then was dried over anhydrous magnesium sulfate. After filtration, the solvent was distilled off under reduced pressure, and the residue was purified by silica gel column chromatography. Thus, 6.54 g of an intermediate 11-13 was obtained. Yield: 91.8%.

(Synthesis of Polymer 11)

Compound (11-A) was synthesized using compound (1-C) by making reference to Example 1 of US Patent Application No. 2008/0121281 A1.

Polymer 11 was synthesized in the same manner as in Example 7, except that 0.12 g of compound (1-C) was changed to 0.11 g of intermediate 11-13, and 0.15 g of compound (7-A) was changed to 0.10 g of compound (11-A). Yield amount: 0.10 g.

The polymer 11 was subjected to an analysis of molecular weight by GPC, and the weight average molecular weight (Mw) calculated relative to standard polystyrenes was 20,300. The ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) was 1.47. Similarly, the absorption spectrum of the coating film of polymer 11 was measured, and it was found that λmax was 690 nm.

Example 12 Synthesis of Polymer 12

Polymer 12 was synthesized as follow.

Compound (12-B) was synthesized using compound 12-A (synthesized by the method described in the specification of US Patent Application No. 2009/0326187 A1) according to a method known.

Polymer 12 was synthesized in the same manner as in Example 7, except that 0.15 g of compound (7-A) was changed to 0.11 g of compound (12-B). Yield amount: 0.10 g.

The polymer 12 was subjected to an analysis of molecular weight by GPC, and the weight average molecular weight (Mw) calculated relative to standard polystyrenes was 19,500. The ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) was 1.49. Similarly, the absorption spectrum of the coating film of polymer 12 was measured, and it was found that λmax was 680 nm.

Here, polymer 1 is an example polymer A-1; polymer 2 is an example polymer A-6; polymer 3 is an example polymer A-16; polymer 4 is an example polymer A-23; polymer 5 is an example polymer A-17; polymer 6 is an example polymer A-24; polymer 7 is an example polymer B-9; polymer 8 is ais an example polymer B-1; polymer 9 is an example polymer B-11; polymer 10 is an example polymer B-12; polymer 11 is an example polymer 10; and polymer 12 is an example polymer B-9.

(Synthesis of Comparative Polymers)

Comparative polymers A to D were synthesized as follow.

(Synthesis of Comparative Polymer A)

The following comparative polymer A of cyclopentadithiazole was synthesized by the method described in WO 2008/067023 (p. 12-13).

The comparative polymer A was subjected to an analysis of molecular weight by GPC, and the weight average molecular weight (Mw) calculated relative to standard polystyrenes was 18,300. The ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) was 1.44. Similarly, the absorption spectrum of the coating film of comparative polymer A was measured, and it was found that λmax was 660 nm.

(Synthesis of Comparative Polymer B)

The following comparative polymer B was synthesized by the method described in Example 1 of JP-T-2010-507233.

The comparative polymer B was subjected to an analysis of molecular weight by GPC, and the weight average molecular weight (Mw) calculated relative to standard polystyrenes was 22,000. The ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) was 1.47. Similarly, the absorption spectrum of the coating film of comparative polymer B was measured, and it was found that λmax was 580 nm.

(Synthesis of Comparative Co-Polymer C)

Comparative co-polymer C having a structure described in the right side was synthesized by the method described in WO 2008/067023 (p. 12-13).

The comparative co-polymer C was subjected to an analysis of molecular weight by GPC, and the weight average molecular weight (Mw) calculated relative to standard polystyrenes was 21,600. The ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) was 1.43. Similarly, the absorption spectrum of the coating film of comparative polymer B was measured, and it was found that λmax was 660 nm.

(Synthesis of Comparative Co-Polymer D)

Comparative co-polymer D having a structure described in the right side was synthesized by the method described in Example 3 of JP-T-2010-507233.

The comparative co-polymer D was subjected to an analysis of molecular weight by GPC, and the weight average molecular weight (Mw) calculated relative to standard polystyrenes was 19,100. The ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) was 1.38. Similarly, the absorption spectrum of the coating film of comparative polymer B was measured, and it was found that λmax was 570 nm.

(Production of Photovoltaic Cell)

Photovoltaic cells were formed on glass ITO substrates by the following procedure, using polymers 1 to 12 and comparative polymers A to D.

On a clean, UV-ozone-treated ITO glass substrate, a PEDOT:PSS (CleviosP VP AI4083 of H.C. Stark GmbH) layer to be used as a hole transport layer was spin-coated and dried for 15 minutes at 120° C.

Subsequently, a mixture (mass ratio 1:1) of one of the p-type semiconductor polymers synthesized as the polymers 1 to 12 and comparative polymers A to D, and PC61BM ([60]PCBM manufactured by Solenne BV) was dissolved in o-dichlorobenzene, and then the solution was spin coated on the PEDOT:PSS layer and dried for 15 minutes at 120° C. Thus, a photoelectric conversion layer was formed.

Furthermore, a dehydrated ethanol solution (2 mass %) of titanium isopropoxide (manufactured by Sigma-Aldrich Co.) was spin coated on this photoelectric conversion layer, and the solution was dried for one hour at room temperature. Thus, an electron transport layer of a titanium oxide layer was formed.

Thereafter, an upper electrode was formed by high vacuum deposition of aluminum, and thereby a photovoltaic element was obtained.

At this time, two kinds of elements, namely a 2-mm square element and a 20-mm square element, were produced by changing the size of the glass ITO substrate used, and the pattern size of the ITO and deposited aluminum.

(Evaluation of Photovoltaic Cell)

1) Current Density-Voltage (J-V) Characteristics of Element

The 2-mm square element and the 20-mm square element respectively produced as described above were subjected to a performance evaluation as follows.

For the elements thus obtained, the current density-voltage (J-V) characteristics of the elements were evaluated using a SMU2400 type I-V measuring apparatus manufactured by Keithley Instruments, Inc. in a nitrogen atmosphere (oxygen concentration: 1 ppm or less, moisture concentration: 1 ppm or less). Filtered xenon lamp light from a solar simulator manufactured by Oriel (Oriel) Instruments Corp. was used, and an AM1.5G spectrum of 100 mW/cm² was approximated. The short circuit current (Jsc), open circuit voltage (Voc), fill factor (FF) and power generation efficiency (η) obtained in the apparatus are presented in the following Table 1.

2) Retention Ratio of Power Generation Efficiency Exposed to Atmosphere

The 2-mm square element obtained as described above was exposed to the light-shielded atmosphere (23° C., 50% RH) for 72 hours, and thereafter, the current density-voltage (J-V) characteristics of the element were evaluated in the same manner as in the above section 1).

These results are presented in the following Table 1.

TABLE 1 photoelectric 2-mm square element 20-mm square conversion 2-mm square element (after exposure to Element layer, (inicial) the atmosphere) (inicial) Sample polymer λmax Jsc Voc FF η η Retention η Retention No. examples [nm] [mA/cm²] [V] [%] [%] [%] ratio [%] [%] ratio [%] Remarks 1 polymer 1 670 10.3 0.70 54 3.9 3.3 85 3.4 87 This invention 2 polymer 2 680 10.5 0.70 55 4.0 3.4 84 3.6 89 This invention 3 polymer 3 630 9.8 0.69 54 3.7 3.1 85 3.0 82 This invention 4 polymer 4 630 9.2 0.74 53 3.6 3.2 89 3.0 83 This invention 5 polymer 5 620 9.1 0.76 55 3.8 3.5 92 3.3 87 This invention 6 polymer 6 710 9.8 0.70 53 3.6 3.1 85 3.1 85 This invention 7 polymer 7 640 10.7 0.68 54 3.9 3.3 84 3.3 84 This invention 8 polymer 8 630 10.5 0.70 50 3.7 3.1 84 3.0 82 This invention 9 polymer 9 620 10.6 0.69 52 3.8 3.1 82 3.4 89 This invention 10 polymer 10 510 9.5 0.71 54 3.6 2.9 80 2.9 80 This invention 11 polymer 11 690 11.6 0.70 55 4.5 3.9 87 3.9 87 This invention 12 polymer 12 680 10.9 0.70 54 4.1 3.5 85 3.4 83 This invention 13 comparative 660 9.7 0.68 48 3.2 2.2 69 2.1 66 Comparative polymer A example 14 comparative 580 9.1 0.66 50 3.0 2.0 67 2.0 67 Comparative polymer B example 15 comparative 660 9.5 0.67 52 3.3 2.1 63 2.3 69 Comparative co-polymer C example 16 comparative 570 10.0 0.64 50 3.2 1.5 47 1.8 56 Comparative co-polymer D example

As a result, it can be seen that a solar cell elements using the organic semiconductor polymers of the present invention have high power generation efficiency η, which have a high retention ratio of the power generation efficiency after exposure to the atmosphere, and in which the decrease in the power generation efficiency is small when the element size is increased.

On the other hand, it can be seen that a solar cell elements using the organic semiconductor polymers of Comparative Example have low conversion efficiency η, in which the conversion efficiency η after exposure to the atmosphere is prone to decrease, and in which the decrease in the power generation efficiency is large when the element size is increased.

Having described our invention as related to the present embodiments, it is our intention that the invention not be limited by any of the details of the description, unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the accompanying claims.

This non-provisional application claims priority under 35 U.S.C. §119 (a) on Patent Application No. 2011-080999 filed in Japan on Mar. 31, 2011, which is entirely herein incorporated by reference. 

The invention claimed is:
 1. An organic semiconductor polymer comprising a homopolymer having a structural unit represented by the following Formula (I-1):

wherein R^(1′) and R^(1″) each independently represents an alkyl group or a copolymer having the structural unit represented by the Formula (I-1) and a structural unit selected from the group consisting of structural units represented by the following Formulae (1), (20), (22), (25) and (II):

wherein in Formula (1), R¹¹ and R¹² each represents an alkyl group, R¹³ and R¹⁴ each represents a hydrogen atom;

wherein in Formula (20), R¹⁵ and R¹⁶ each represents an alkyl group;

wherein in Formula (22), R¹⁵ and R¹⁶ each represents an alkyl group;

wherein in Formula (25), R¹⁵ and R¹⁶ each represents a hydrogen atom, and Y² represents a sulfur atom; and

wherein Formula (II), Z¹ and Z² each independently represents S; and Y represents C(R²¹) or N; R represents an alkyl group or an alkylsulfonyl group; and R²¹ represents a hydrogen atom.
 2. A composition for organic semiconductor material, including the organic semiconductor polymer according to claim 1 and an n-type organic semiconductor molecule.
 3. The composition for organic semiconductor material according to claim 2, wherein the n-type organic semiconductor molecule is fullerene or a derivative thereof.
 4. The composition for organic semiconductor material according to claim 3, wherein the fullerene or a derivative thereof is a phenyl-C₆₁-butyric acid ester, a diphenyl-C₆₂-bis(butyric acid ester), a phenyl-C₇₁-butyric acid ester, a phenyl-C₈₅-butyric acid ester, or a thienyl-C₆₁-butyric acid ester.
 5. A photovoltaic cell including the organic semiconductor polymer or the composition for organic semiconductor material according to claim
 1. 6. A photovoltaic cell including a layer containing the organic semiconductor polymer or the composition for organic semiconductor material according to claim 1, between a first electrode and a second electrode.
 7. The photovoltaic cell according to claim 6, including a hole transport layer between the first electrode and the layer containing the organic semiconductor polymer or the composition for organic semiconductor material.
 8. The photovoltaic cell according to claim 6, including an electron transport layer between the second electrode and the layer containing the organic semiconductor polymer or the composition for organic semiconductor material.
 9. The photovoltaic cell according to claim 6, wherein the first electrode is a transparent electrode.
 10. The photovoltaic cell according to claim 6, wherein the second electrode is a metal electrode.
 11. A polymer having a structural unit represented by the following Formula (I-1):

wherein R^(1′) and R^(1″) each independently represent an alkyl group or a copolymer having the structural unit represented by the Formula (I-1) and a structural unit selected from the group consisting of structural units represented by the following Formulae (1), (20), (22), (25) and (II):

wherein in Formula (1), R¹¹ and R¹² each represents an alkyl group, R¹³ and R¹⁴ each represents a hydrogen atom;

wherein in Formula (20), R¹⁵ and R¹⁶ each represents an alkyl group;

wherein in Formula (22), R¹⁵ and R¹⁶ each represents an alkyl group;

wherein in Formula (25), R¹⁵ and R¹⁶ each represents a hydrogen atom, and Y² represents a sulfur atom; and

wherein Formula (II), Z¹ and Z² each independently represents S; and Y represents C(R²¹) or N; R represents an alkyl group or an alkylsulfonyl group; and R²¹ represents a hydrogen atom. 